Leadframe and method for manufacturing resin-molded semiconductor device

ABSTRACT

In a leadframe for an LGA package, a lead member is pressed downward to form a land lead with a half-cut portion and a land portion. The land portion, whose bottom will be a land electrode, is inclined at a predetermined angle and the bottom of the land portion is made lower than that of a lead. Thus, in a resin molding process using a seal sheet, the land electrode is forced into, and strongly adhered to, the seal sheet when pressure is applied through dies, and no resin encapsulant reaches the land electrode. As a result, no resin bur will be left on the land electrode of the land lead.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a leadframe, which includesleads with land electrodes functioning as external terminals and canreplace a conventional leadframe with beam-like leads. The presentinvention also relates to a method for manufacturing a land-grid-array(LGA) resin-molded semiconductor device, in which a semiconductor chipis bonded onto the leadframe and the assembly is molded with a resinencapsulant.

[0002] In recent years, to catch up with rapidly advancing downsizing ofelectronic units, it has become increasingly necessary to assemblesemiconductor components, like resin-molded semiconductor devices, at ahigher and higher density. In response, sizes and thicknesses ofsemiconductor components have also been noticeably reduced. In parallelwith this downsizing trend, the number of pins needed for a singleelectronic unit is also increasing day after day. To meet these demands,resin-molded semiconductor devices of a greatly shrunken size and with adrastically reduced thickness should now be assembled at an even higherdensity.

[0003] Hereinafter, a conventional leadframe for a resin-moldedsemiconductor device will be described.

[0004]FIG. 22 is a plan view illustrating the structure of aconventional leadframe. As illustrated in FIG. 22, the leadframeincludes rectangular die pad 102, support leads 103, beam-like innerleads 104, outer leads 105 and tie bars 106, all of these members beingprovided inside a frame rail 101. The die pad 102 is used for mounting asemiconductor chip thereon. The support leads 103 support the die pad102. The inner leads 104 will be electrically connected to thesemiconductor chip with some connection members like metal fine wires.The outer leads 105 are joined to the respective inner leads 104 and tobe connected to external terminals. And the tie bars 106 are providedfor joining and fixing the outer leads 105 together and for preventing aresin encapsulant from overflowing during a resin molding process.

[0005] It should be noted that normally the leadframe does not consistof the single pattern shown in FIG. 22, but is made up of a plurality ofsuch patterns, which are arranged and connected together bothhorizontally and vertically.

[0006] Next, a known resin-molded semiconductor device will bedescribed. FIG. 23 is a cross-sectional view illustrating a resin-moldedsemiconductor device including the leadframe shown in FIG. 22.

[0007] As shown in FIG. 23, a semiconductor chip 107 has been bondedonto the die pad 102 of the leadframe and electrically connected to theinner leads 104 with metal fine wires 108. The semiconductor chip 107 onthe die pad 102, the inner leads 104 and so on have been molded with aresin encapsulant 109. The outer leads 105 protrude from the side facesof the resin encapsulant 109 and have had their outer ends bentdownward.

[0008] Next, a method for manufacturing the resin-molded semiconductordevice will be described with reference to FIGS. 23 and 24. First, thesemiconductor chip 107 is bonded, with an adhesive, onto the die pad 102of the leadframe. This process step is called “die bonding”. Next, thesemiconductor chip 107 is connected to the respective inner ends of theinner leads 104 with the metal fine wires 108. This process step iscalled “wire bonding”. Subsequently, the semiconductor chip 107 and aportion of the leadframe inside the tie bars 106 (i.e., the inner leads104 and so on) are molded with the resin encapsulant 109 such that theouter leads 105 protrude outward. This process step is called “resinmolding”. Finally, the tie bars 106 are cut off at the boundary betweenthe tie bars 106 and the resin encapsulant 109 to separate the outerleads 105 from each other and remove the frame rail 101, and therespective outer ends of the outer leads 105 are bent. This process stepis called “tie bar cutting and bending”. In this manner, a resin-moldedsemiconductor device with the structure shown in FIG. 23 is completed.In FIG. 24, the dashed line indicates a region where the assembly ismolded with the resin encapsulant 109.

[0009] As described above, the number of devices that should beintegrated within a single semiconductor chip, or the number of pins perchip, has been on the rise these days. Thus, the number of outer leadsshould also be increased to catch up with this latest trend. That is tosay, the number of inner leads, which are joined to the outer leads,should preferably be increased to cope with such an implementation.However, the width of the inner (or outer) lead has a processable limit.Thus, as the number of inner (or outer) leads is increased, the overallsize of the leadframe and that of the resulting resin-moldedsemiconductor device also increase. In view of these states in the art,it is difficult to realize a downsized and thinned resin-moldedsemiconductor device. On the other hand, if only the number of innerleads is increased to cope with the rise in the number of pins neededfor a semiconductor chip while using a leadframe of substantially thesame size, then the width of a single inner lead should be furtherreduced. In such a case, however, it is much more difficult to performvarious process steps for forming the leadframe, like etching, asoriginally designed.

[0010] Recently, face-bonded semiconductor devices, such as ball gridarray (BGA) types and land grid array (LGA) types, are also available.In the semiconductor device of any of these types, first, asemiconductor chip is mounted onto a carrier (e.g., a printed wiringboard) including external electrodes (e.g., ball electrodes or landelectrodes) on its bottom. Next, the semiconductor chip is electricallyconnected to the external electrodes. And then the chip and itsassociated members are molded with a resin encapsulant on the uppersurface of the carrier. The semiconductor device of this face-bondedtype, which is mounted directly on a motherboard on the bottom, will bea mainstream product in the near future. Accordingly, it is now clearthat the conventional leadframe and resin-molded semiconductor deviceusing the leadframe will soon be out of date under the circumstancessuch as these.

[0011] Also, the conventional resin-molded semiconductor device includesouter leads protruding outward from the side faces of a resinencapsulant, and is supposed to be mounted onto a motherboard by bondingthe outer leads to the electrodes on the motherboard. Accordingly, theconventional device cannot be mounted onto the board so reliably as thesemiconductor devices of the BGA and LGA types. Nevertheless, thesemiconductor devices of the BGA and LGA types are expensive, becausethese devices use a printed wiring board.

SUMMARY OF THE INVENTION

[0012] It is therefore an object of the present invention to provide aleadframe effectively applicable to a resin-molded semiconductor device,in which external terminals are arranged and exposed in lines on thebottom of the package with almost no resin bur left on.

[0013] It is another object of the present invention to provide a methodfor manufacturing the resin-molded semiconductor device using theleadframe.

[0014] An inventive leadframe includes a frame rail, a die pad, supportleads and first and second groups of leads. The frame rail is made of ametal plate. The die pad is used for mounting a semiconductor chipthereon, and disposed approximately in a center region of an opening ofthe frame rail. One end of each of the support leads supports the diepad, while the other end thereof is connected to the frame rail. One endof each of the leads of the first group extends toward the die pad atleast partially, while the other end thereof is connected to the framerail. The bottom of each lead of the first group is used as a landelectrode of a first group. One end of each of the leads of the secondgroup extends toward the die pad and is closer to the die pad than theend of the lead of the first group is, while the other end thereof isconnected to the frame rail. Part of the bottom of each lead of thesecond group is used as a land electrode of a second group. The firstand second groups of land electrodes are arranged in two lines. At leastpart of each lead of the second group has been pressed down by half-cutpressworking such that the bottom of each land electrode of the secondgroup is lower than that of each land electrode of the first group. Thatpart of the lead of the second group is inclined downward.

[0015] If a resin-molded semiconductor device is formed using thisleadframe, a land grid array (LGA) package can be obtained. That is tosay, external terminals will be arranged in two lines on the bottom ofthis package. Specifically, the second group of land electrodes of landleads (i.e., the second group of leads) forms the inner one of the two,while the first group of land electrodes of leads (i.e., the first groupof leads) forms the outer line. At least part of each lead of the secondgroup has been pressed down by half-cut pressworking such that thebottom of each land electrode of the second group is lower than that ofeach land electrode of the first group. In addition, that part of thelead of the second group is inclined downward. Accordingly, when apressure is applied to these leads, the bottom of the land electrode ofthe second group is forced into, and strongly adhered to, a seal sheet,and no resin encapsulant reaches the land electrode. As a result, apackage, including external terminals with no resin bur left on, can beobtained.

[0016] In one embodiment of the present invention, that part of the leadof the second group is preferably inclined at an angle between 3 and 15degrees with a principal surface of the leadframe.

[0017] An inventive method for manufacturing a resin-moldedsemiconductor device includes the step of a) preparing a leadframe. Theleadframe includes a frame rail, a die pad, support leads and first andsecond groups of leads. The frame rail is made of a metal plate. The diepad is used for mounting a semiconductor chip thereon, and disposedapproximately in a center region of an opening of the frame rail. Oneend of each of the support leads supports the die pad, while the otherend thereof is connected to the frame rail. One end of each of the leadsof the first group extends toward the die pad at least partially, whilethe other end thereof is connected to the frame rail. The bottom of eachlead of the first group is used as a land electrode of a first group.One end of each of the leads of the second group extends toward the diepad and is closer to the die pad than the end of the lead of the firstgroup is, while the other end thereof is connected to the frame rail.Part of the bottom of each lead of the second group is used as a landelectrode of a second group. The first and second groups of landelectrodes are arranged in two lines. At least part of each lead of thesecond group has been pressed down by half-cut pressworking such thatthe bottom of each land electrode of the second group is lower than thatof each land electrode of the first group. And that part of the lead ofthe second group is inclined downward. The method further includes thesteps of: b) bonding a semiconductor chip onto the die pad of theleadframe prepared; c) connecting electrode pads, which are formed onthe principal surface of the semiconductor chip bonded to the die pad,to respective upper surfaces of the first and second groups of leads ofthe leadframe with metal fine wires; d) adhering a seal sheet to atleast the bottoms of the die pad and the first and second groups ofleads on the backside of the leadframe; e) molding an upper part of theleadframe, the semiconductor chip, the die pad and the metal fine wirestogether with a resin encapsulant, while applying a pressure to at leastthe ends of the first and second groups of leads to press the first andsecond groups of land electrodes against the seal sheet; and f)stripping the seal sheet from the leadframe after the step e) has beenperformed.

[0018] In this method, a resin-molded semiconductor device is formed bymounting a semiconductor chip on the leadframe, connecting the chip tothe leads (whose bottoms will be land electrodes as external terminals)with metal fine wires and then molding these members together with aresin encapsulant. In this manner, a land grid array (LGA) package canbe obtained. That is to say, external terminals will be arranged in twolines on the bottom of the resin-molded semiconductor device (or thepackage). Specifically, the second group of land electrodes of landleads (i.e., the second group of leads) forms the inner one of the two,while the first group of land electrodes of leads (i.e., the first groupof lead) forms the outer line. Part of each lead of the second group hasbeen pressed down by half-cut pressworking such that the bottom of theland electrode of the second group is lower than that of the landelectrode of the first group. In addition, that part of the lead of thesecond group is inclined downward. Accordingly, when a pressure isapplied to these leads, the bottoms of the land electrodes of the secondgroup are forced into, and strongly adhered to, a seal sheet. That is tosay, it is possible to prevent the leads of the second group from beinglifted by the pressure applied during the injection of the resinencapsulant, and no resin encapsulant reaches the land electrodes. As aresult, no resin bur will be left on the land electrodes of the secondgroup.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a plan view illustrating a leadframe according to thepresent invention.

[0020]FIG. 2(a) is a plan view illustrating a land lead and a leadaccording to a first embodiment of the present invention.

[0021]FIG. 2(b) is a cross-sectional view of the lead taken along theline IIb-IIb shown in FIG. 2(a); and

[0022]FIG. 2(c) is a cross-sectional view of the land lead taken alongthe line IIc-IIc shown in FIG. 2(a).

[0023]FIG. 3 is a top view of a resin-molded semiconductor deviceaccording to the present invention.

[0024]FIG. 4 is a bottom view of the inventive resin-moldedsemiconductor device.

[0025]FIG. 5 is a cross-sectional view of the resin-molded semiconductordevice taken along the line V-V shown in FIGS. 3 and 4.

[0026]FIG. 6 is a cross-sectional view of the resin-molded semiconductordevice taken along the line VI-VI shown in FIGS. 3 and 4.

[0027]FIG. 7 is a cross-sectional view illustrating how the resin-moldedsemiconductor device may be mounted on a motherboard.

[0028]FIGS. 8, 9, 10, 11, 12 and 13 are cross-sectional viewsillustrating respective process steps for manufacturing the resin-moldedsemiconductor device according to the present invention.

[0029] FIGS. 14(a) and 14(b) are respectively partial plan view andpartial cross-sectional view illustrating, on a larger scale, part ofthe land lead according to the first embodiment.

[0030]FIGS. 15 and 16 are partial cross-sectional views illustrating howrespective members of the resin-molded semiconductor device may bemolded with a resin encapsulant in the first embodiment.

[0031]FIG. 17 is a partial cross-sectional view of the resin-moldedsemiconductor device of the first embodiment, in which resin bur is leftduring a resin molding step.

[0032] FIGS. 18(a) and 18(b) are respectively plan view andcross-sectional view illustrating a land lead for a leadframe accordingto a second embodiment of the present invention.

[0033]FIG. 19 is a cross-sectional view illustrating how a seal sheet isattached to a land lead of the leadframe according to the secondembodiment.

[0034]FIG. 20 is a cross-sectional view illustrating how to place aleadframe into press dies to form the land lead of the leadframeaccording to the second embodiment.

[0035]FIG. 21 is a cross-sectional view illustrating the land lead thathas been formed out of the leadframe according to the second embodiment.

[0036]FIG. 22 is a plan view illustrating a conventional leadframe.

[0037]FIG. 23 is a cross-sectional view illustrating a conventionalresin-molded semiconductor device.

[0038]FIG. 24 is a plan view of the conventional resin-moldedsemiconductor device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] Hereinafter, preferred embodiments of the present invention willbe described with reference to the accompanying drawings.

[0040] Embodiment 1

[0041] A first embodiment of the present invention relates to aleadframe, a resin-molded semiconductor device including the leadframeand a method for manufacturing the device.

[0042] First, a leadframe according to the first embodiment will bedescribed.

[0043]FIG. 1 is a plan view illustrating a leadframe according to thepresent invention. FIG. 2(a) is a plan view illustrating a land lead 4and a lead 5 according to the first embodiment. FIG. 2(b) is across-sectional view of the lead 5 taken along the line IIb-IIb shown inFIG. 2(a). And FIG. 2(c) is a cross-sectional view of the land lead 4taken along the line IIc-IIc shown in FIG. 2(a). In FIG. 1, the two-dotchain indicates a molding region where a semiconductor chip will bemounted on the leadframe of this embodiment and these members will bemolded together with a resin encapsulant.

[0044] As shown in FIGS. 1, 2(a), 2(b) and 2(c), the leadframe of thisembodiment is a platelike member made of a metal like copper or Alloy 42for use in normal leadframes. The leadframe includes die pad 1, framerail 2, support leads 3, linear land leads 4 and linear leads 5. The diepad 1 is used for mounting a semiconductor chip thereon. One end of eachsupport lead 3 is connected to the frame rail 2, while the other endthereof supports one of the four corners of the die pad 1. One end ofeach of the land leads 4 and leads 5 extends toward the die pad 1, whilethe other end thereof is connected to the frame rail 2. The land leads 4and the leads 5 are equivalent to the second and first groups of leads,respectively, as defined in the appended claims. The respective bottomsof the land leads 4 and leads 5 are used as external terminals (or landportions). In addition, not only the bottom but also the outer side faceof each lead 5 serve as an external terminal that can be connected to amotherboard. The inner free end of the land lead 4 is closer to the diepad 1 than that of the lead 5 is.

[0045] Specifically, the die pad 1 includes a circular, protrudingportion 6. The protruding portion 6 protrudes upward from around thecenter of the upper surface of the die pad 1 (as will be described laterwith reference to FIG. 5). The protruding portion 6 can be formed byhalf-cutting part of a flat plate for the die pad 1 and making that partprotrude upward by pressworking. A semiconductor chip will actually besupported on this protruding portion 6. Thus, when the semiconductorchip is mounted on that portion 6, a gap will be created between thesurface of the die pad 1, except for the protruding portion 6, and thebackside of the semiconductor chip. A groove 7 is also formed in theupper surface of the die pad 1 to surround the protruding portion 6.Accordingly, when the semiconductor chip is bonded onto the die pad 1and molded with a resin encapsulant, the resin encapsulant will enterthe groove 7. In the illustrated embodiment, the groove 7 is formed inan annular shape. When the semiconductor chip is molded with a resinencapsulant after having been bonded and fixed onto the protrudingportion 6 of the die pad 1 with an adhesive, the resin encapsulant isreceived at the groove 7. Accordingly, even if a stress, resulting fromthermal expansion, has peeled the resin encapsulant off the surface ofthe die pad 1, that peeled part of the resin encapsulant can be trappedat the groove 7, thus preventing the reliability of the resin-moldedsemiconductor device from decreasing. Although the groove 7 is annularaccording to this embodiment, the groove 7 may also be in the shape of adiscontinued ring. Also, two or more grooves 7, e.g., three or fourgrooves, may be formed. In short, the shape and number of the groove(s)may be appropriately selected depending on the size of the die pad 1 andthat of the semiconductor chip to be mounted thereon.

[0046] Also, in this embodiment, the land leads 4 and leads 5 arearranged alternately and parallelly when connected to the frame rail 2.As viewed from above, the inner free ends of the land leads 4 and leads5 are arranged like a hound's-tooth check. And the respective inner endsof the land leads 4 are closer to the die pad 1 than those of the leads5 are. This arrangement is selected such that when the semiconductorchip is mounted and molded with a resin encapsulant, the bottoms ofthese inner ends of the land leads 4 and leads 5 are arranged like ahound's-tooth check on the bottom of the package. And these bottoms willbe used as external terminals arranged in two lines. As shown in FIG.2(a), the land lead 4 is a linear lead including a curved land portion 8at its end functioning as an external terminal. Also, as shown in FIG.2(c), the land portion 8 has an original thickness, which is greaterthan the thickness of the other portions that has been reduced byhalf-etching.

[0047] More specifically, the land portion 8 of the land lead 4protrudes downward, and the upper surface of the land lead 4 is greaterin area than the lower surface thereof. In FIG. 1, the dashed lineindicates the land portion 8 on the bottom of the land lead 4. In FIG.2(a), the cross-hatched regions indicate the half-etched portions of theland lead 4. Like the land lead 4, the outer edge of the lead 5 also hasits thickness reduced by half etching, a wide portion 9 is provided atthe end of the lead 5 and a groove 10 is formed at around the root ofthe wide portion 9 as shown in FIGS. 2(a) and 2(b). A land portion witha curved edge is also formed on the bottom of the lead 5. In FIGS. 1 and2(a), the hatched region indicates the groove 10. If a semiconductorchip is mounted on the leadframe of this embodiment and molded with aresin encapsulant, then just one side of the package will be sealed andthe bottom and the side face of the lead 5 will be exposed. Accordingly,unlike the conventional fully-molded package, some stress might beapplied to the leads 5 during resin molding or after the package hasbeen mounted on the motherboard. Even so, that stress can be cushionedby the grooves 10, thus preventing the metal fine wires from beingdisconnected and keeping the assembled product highly reliable. In thiscase, the surface of the land portion 8 of the land lead 4 and the wideportion 9 of the lead 5 will be bonding pads to which the metal finewires will be connected.

[0048] In the leadframe of this embodiment, the land leads 4 and leads 5are both linear leads, and the land portion 8 on their bottom has acurved edge. Also, since the land leads 4 and leads 5 are arrangedalternately, the land portions 8 of these leads 4 and 5 form ahound's-tooth check on the bottom of the package.

[0049] As shown in FIGS. 4 and 5, a rectangular (or annular) groove 11is formed in the bottom of the die pad 1 of the leadframe according tothe first embodiment. As can be seen from the bottom view illustrated inFIG. 4, the bottom of the protruding portion 6 is encircled with thegroove 11. When the package is bonded onto a motherboard with solder orany other bonding member applied to the bottom of the die pad 1, thesolder does not expand more than necessarily, since the groove 11receives the solder. As a result, the package can be mounted moreaccurately. In addition, the stress applied by the die pad 1 itself,resulting from the heat dissipated from the semiconductor chip, can alsobe cushioned. In the illustrated embodiment, just one groove 11 isprovided. Optionally, to further improve the mounting accuracy, anotherone, two or more annular grooves may be additionally formed around theouter periphery of the bottom of the die pad 1.

[0050] Furthermore, each of the support leads 3 may have a dummy landportion or bent portion.

[0051] The number of the land leads 4 or leads 5 may be appropriatelyselected depending on the number of pins of a semiconductor chip to bemounted on the leadframe.

[0052] Also, according to the first embodiment, the surface of theleadframe may plated with a stack of metal layers, e.g., nickel (Ni),palladium (Pd) and gold (Au) layers, if necessary.

[0053] When a resin-molded semiconductor device is formed by mounting asemiconductor chip on the leadframe of this embodiment, connecting thechip to the leads with metal fine wires and molding these memberstogether with a resin encapsulant, a land grid array (LGA) package canbe obtained. That is to say, two lines of external terminals arearranged like a hound's-tooth check on the bottom of the resin-moldedsemiconductor device (or the package). Specifically, as shown in FIG. 4,the land portions 8 of the land leads 4 with a curved edge have theirbottoms exposed along the inner one of these two lines, while those ofthe leads 5 with a curved edge also have their bottoms exposed along theouter line.

[0054] A resin encapsulant might peel off after the members have beenmolded with the resin encapsulant while a resin-molded semiconductordevice is being formed using the leadframe of the first embodiment.However, that peeled resin encapsulant can be received at the groove 7formed in the upper surface of the die pad 1. As a result, theresin-molded semiconductor device can be greatly reliable. In addition,the heat can be dissipated from the device more efficiently, the packagecan be bonded onto a motherboard with solder more accurately and thearea of a mountable semiconductor chip can be increased.

[0055] Next, a resin-molded semiconductor device, which has been formedby using the leadframe shown in FIGS. 1, 2(a), 2(b) and 2(c), will bedescribed with reference to the accompanying drawings. FIGS. 3 and 4 arerespectively top and bottom views of a resin-molded semiconductor deviceaccording to the first embodiment. FIGS. 5 and 6 are cross-sectionalviews of the device taken along the lines V-V and VI-VI, respectively,shown in FIGS. 3 and 4.

[0056] As shown in FIGS. 3, 4, 5 and 6, the resin-molded semiconductordevice of the first embodiment includes the die pad 1, semiconductorchip 12, leads 5, land leads 4, metal fine wires 14 and resinencapsulant 15. As described above, the die pad 1 has the protrudingportion 6 and groove 7 on its upper surface and the annular groove 11 onits bottom. The groove 7 surrounds the protruding portion 6 on the uppersurface and may be circular, rectangular or any other complex shape. Thesemiconductor chip 12 has been bonded onto the protruding portion 6 ofthe die pad 1 with a conductive adhesive (not shown) such as silverpaste. Each of the leads 5 has the groove 10 on its upper surface andhas its bottom exposed on the bottom of the package. Each of the landleads 4 extends toward the die pad 1 and the inner end of the land lead4 is closer to the die pad 1 than that of each lead 5 is. Each of theland leads 4 has its bottom exposed on the bottom of the package andused as the land electrode 16. The metal fine wires 14 electricallyconnect the electrode pads (not shown) on the principal surface of thesemiconductor chip 12 to the bonding pads 13 of the land leads 4 andleads 5. And all of these members 1, 12, 5, 4 and 14 are molded togetherwithin the resin encapsulant 15 except for the bottom of the die pad 1,respective bottoms of the land leads 4 and leads 5 and respective outerside faces of the leads 5. The respective bottoms of the land leads 4,exposed on the bottom of the resin encapsulant 15, and the respectiveside faces and bottoms of the leads 5, exposed on the bottom and sidefaces of the resin encapsulant 15, are used as the land electrodes 16.These land electrodes 16 will be external terminals when the package ismounted onto a motherboard like a printed wiring board. These bottoms ofthe leads 5 and land leads 4 are exposed out of the resin encapsulant 15and arranged in two lines like a hounds'-tooth check. Each of the landelectrodes 16 is exposed and protrudes out of the resin encapsulant 15by about 20 μm, thus providing a standoff height needed in mounting thepackage onto the motherboard. In the same way, the exposed bottom of thedie pad 1 also protrudes out of the resin encapsulant 15. Accordingly,after the package has been mounted onto the motherboard, heat, generatedfrom the semiconductor chip 12, can be dissipated more efficientlytoward the motherboard through the solder joint.

[0057] In addition, the bottom of the die pad 1 is further provided witha concave portion 17. As described above, the half-cut protrudingportion 6 is formed on the upper surface of the die pad 1 bypressworking. Accordingly, the depth of the concave portion 17 issubstantially equal to the height of the protruding portion 6. In theillustrated embodiment, the die pad 1 is made of a metal plate (i.e.,the leadframe) with a thickness of 200 μm. And the height of theprotruding portion 6 may be between 140 μm and 180 μm, i.e., 70 to 90%of the thickness of the metal plate.

[0058] The area of the bonding pad 13 of the land leads 4 and leads 5 ispreferably large enough to enable wire bonding, e.g., 100 μm² or more,and small enough to make the electrodes arrangeable at a high densityneeded for realizing a downsized and thinned resin-molded semiconductordevice.

[0059] By utilizing the structure of this embodiment, a high-densityface-bonded resin-molded semiconductor device, which can cope with therecent increase in number of pins, is implementable.

[0060] According to the present invention, the thickness of the package(or the resin-molded semiconductor device) itself can be reduced to assmall as 1 mm or less, e.g., 800 μm.

[0061] In this manner, the resin-molded semiconductor device of thefirst embodiment can be a land grid array (LGA) package. That is to say,external terminals are arranged in two lines like a hound's-tooth checkon the bottom of the package. Specifically, the land electrodes 16 ofthe land leads 4 have their bottoms exposed along the inner one of thetwo, while the land electrodes 16 of the leads 5 also have their bottomsexposed along the other outer line. Also, even if the resin encapsulant15 has peeled off between the backside of the semiconductor chip 12 andthe upper surface of the die pad 1, that peeled resin encapsulant can bereceived at the groove 7 formed in the upper surface of the die pad 1.As a result, the resin-molded semiconductor device can be kept reliable.In addition, the heat can be dissipated from the device moreefficiently, the package can be bonded with solder onto a motherboardmore accurately and the area of a mountable semiconductor chip can beincreased.

[0062] Furthermore, the resin-molded semiconductor device of the firstembodiment is an LGA type device that can be bonded onto a motherboardusing only the leadframe and does not need any additional wiring orcircuit board necessary for the conventional LGA device. And yet theinventive device can be bonded onto the motherboard more strongly.

[0063]FIG. 7 is a cross-sectional view illustrating how the resin-moldedsemiconductor device of the first embodiment shown in FIG. 6 may bemounted on a motherboard. As shown in FIG. 7, the device of thisembodiment may be mounted onto a motherboard 18 (e.g., a printed wiringboard) by bonding the land electrodes 16, exposed on the bottom of thepackage, to the motherboard 18 with an adhesive 19 such as solder. Theland electrodes 16 of the land leads 4 are bonded to the motherboard 18with the adhesive 19 that has been attached only to the bottoms of theelectrodes 16 (not shown in FIG. 7). On the other hand, as shown in FIG.7, the land electrodes 16 of the leads 5 are bonded to the motherboard18 with the adhesive 19 that has been attached not only to the bottomsof the electrodes 16 but also to the side faces of the leads 5. This ispossible because the outer side faces of the leads 5 are exposedaccording to this embodiment.

[0064] In a known LGA resin-molded semiconductor device, only thebottoms of land electrodes are bonded to a motherboard with an adhesive.In contrast, according to this embodiment, the outer side faces of theleads 5, which form the outer line of land electrodes 16 on the bottomof the package, are exposed out of the package (or the resin encapsulant15). Thus, it is possible to apply the adhesive 19 to those side facesas well. That is to say, the leads 5, forming the outer line of landelectrodes 16, can be bonded to the motherboard 18 with the adhesive 19on two sides, i.e., their bottoms and their outer side faces. As aresult, the package can be bonded onto the motherboard more strongly andmore reliably.

[0065] According to this embodiment, the land electrodes are arranged intwo lines that correspond to the land leads and leads, respectively. Inaddition, the land electrodes, arranged along the outer line, have theirside faces exposed out of the resin encapsulant. Thus, it is possible toprovide additional portions to be connected to the motherboard for theside faces of the package. A two-side (i.e., bottom and side faces)bonding structure like this has never been applied to the bonding of thepackage to the motherboard by any other known LGA resin-moldedsemiconductor device using a leadframe. Thus, the inventive structurerealizes much more reliable bonding and is very advantageous.

[0066] When a resin-molded semiconductor device is formed by mounting asemiconductor chip on the leadframe of this embodiment and molding themtogether with a resin encapsulant, land electrodes, electricallyconnected to the chip, can be arranged in two line or like ahound's-tooth check on the bottom of the package. In this manner, aface-bonded semiconductor device can be obtained. Accordingly, comparedto the known bonding technique using leads, the package can be bonded tothe motherboard much more reliably.

[0067] In addition, the inventive resin-molded semiconductor device doesnot include any circuit board with land electrodes unlike a known BGAsemiconductor device. Instead, according to the present invention, anLGA semiconductor device is formed with a metal plate shaped into aleadframe. Thus, the inventive semiconductor device is far moreadvantageous than the known BGA semiconductor device inmass-productivity and manufacturing cost.

[0068] Next, an exemplary method for manufacturing the inventiveresin-molded semiconductor device will be described with reference tothe accompanying drawings. FIGS. 8, 9, 10, 11, 12 and 13 arecross-sectional views illustrating respective process steps formanufacturing the resin-molded semiconductor device according to thefirst embodiment. In the following description, a method formanufacturing an LGA resin-molded semiconductor device using theleadframe shown in FIG. 1 will be exemplified. Also, only thecross-sectional views taken along the line V-V shown in FIGS. 3 and 4(i.e., cross sections passing the land leads 4) will be referred to forconvenience sake. Accordingly, no leads 5 are illustrated in any ofFIGS. 8 through 13.

[0069] First, as shown in FIG. 8, a leadframe, including the frame rail,die pad 1, support leads (not shown in FIG. 8), leads (not shown in FIG.8) and land leads 4, is prepared. The frame rail is formed out of ametal plate. The die pad 1 for mounting a semiconductor chip thereon isdisposed within the opening of the frame rail. One end of each supportlead supports the die pad 1, while the other end thereof is connected tothe frame rail. The bottoms of the leads will be used as land electrodesthat are arranged in line at regular intervals. Each of these leads hasa wide bonding pad portion, to which a metal fine wire will beconnected, on the surface of its inner end, while the other outer endthereof is connected to the frame rail. A groove is formed near theinner end of each lead. The bottoms of the land leads 4 will also beused as land electrodes. Each of these land leads also has a widebonding pad portion 13, to which a metal fine wire will be connected, onthe surface of its inner end, while the other outer end thereof isconnected to the frame rail. The upper surface of each land lead 4 isgreater in area than the lower surface thereof. And the respective innerends of the leads and land leads 4 are alternately arranged in two lineslike a hound's-tooth check. The die pad 1 has a protruding portion 6 anda circular or rectangular groove 7, surrounding the protruding portion6, on its upper surface, and also has an annular groove 11 and a concaveportion 17 on its lower surface.

[0070] Next, as shown in FIG. 9, a semiconductor chip 12 is mounted andbonded, with a conductive adhesive like silver paste, onto theprotruding portion 6 of the die pad 1 of the leadframe prepared. In thiscase, the semiconductor chip 12 is placed with its circuitry side (orits principal surface) facing upward.

[0071] Then, as shown in FIG. 10, electrode pads, formed on theprincipal surface of the semiconductor chip 12 on the die pad 1, areelectrically connected, with metal fine wires 14, to the bonding pads 13on the upper surfaces of the land leads 4 and leads (not shown) of theleadframe. In the illustrated embodiment, the area of each of thesebonding pads 13, to which the metal fine wire 14 is connected, is 100μm² or more.

[0072] Subsequently, as shown in FIG. 11, a seal tape or seal sheet 20is closely attached to the backside of the leadframe, i.e., to thebottom of the die pad 1, the land electrodes of the land leads 4 and thebottoms of the leads (not shown). The seal sheet 20 used in this processstep is made of a plastic material that is not adhesive to the leadframebut can be easily peeled off after the resin encapsulation. By usingthis seal sheet 20, the resin encapsulant cannot reach the backside ofthe leadframe during a resin molding process step and therefore no resinbur will be deposited on the bottoms of the die pad 1, land leads 4 andleads (not shown). Thus, a water jet process step, which is normallycarried out for deburring purposes after the resin molding, can beomitted.

[0073] Thereafter, as shown in FIG. 12, the exposed upper surface of theleadframe with the die pad 1, the semiconductor chip 12 on theleadframe, metal fine wires 14 and so on, are molded together with aresin encapsulant 15 with the seal sheet 20 attached to the backside.This process step is ordinarily performed by a single-side-moldingtechnique, i.e., transfer molding using a die assembly consisting ofupper and lower dies divided. In this case, since the bottoms of the diepad 1, land leads 4 and leads (not shown) are not covered with the resinencapsulant 15, a “single-side-molded structure” is obtained.Particularly, portions of the land leads 4 and leads, which areconnected to the frame rail 2 (i.e., portions that have not been moldedwith the resin encapsulant 15), are preferably pressed by the upper dieagainst the lower die with the seal sheet 20 interposed therebetween. Inthat case, the resin molding process can be performed with the bottomsof the land leads 4 and leads strongly pressed and forced into the sealsheet 20. As a result, no resin bur will be left on these bottoms and astandoff height is ensured, because these bottoms of the land leads 4and leads will protrude downward from the bottom of the package (i.e.,the bottom of the resin encapsulant 15).

[0074] The seal sheet 20 may be closely attached or adhered to thebackside of the leadframe in any of various manners. For example, theseal sheet 20 may be placed in advance on the lower die of the dieassembly and then attached to the leadframe before the resin moldingprocess is carried out. Alternatively, the seal sheet 20 may be attachedin advance to the leadframe before the resin molding process is carriedout, and then the assembly with the seal sheet may be introduced intothe die assembly and molded with the resin encapsulant.

[0075] Next, as shown in FIG. 13, after the resin molding process isover, the seal sheet 20 is peeled off, for example, and then portions ofthe support leads, land leads 4 and leads, which have been connected tothe frame rail, are cut off. In this process step, these leads are cutoff such that the respective ends of the leads are substantially flushwith the side faces of the resin-molded package. As a result, thebottoms of the land leads 4 and leads become land electrodes 16, theouter side faces of the leads becomes external electrodes and the bottomof the die pad 1 is exposed to easily dissipate heat therefrom.

[0076] By the method for manufacturing a resin-molded semiconductordevice according to this embodiment, a package with a backside structuresuch as that illustrated in FIG. 4 is obtained. Specifically, as thepackage is viewed from below, land electrodes are arranged in two linesalong the four sides of the package. That is to.say, the land electrodes16 of the land leads 4 have their bottoms exposed along the inner line,while the land electrodes of the leads have their bottoms exposed alongthe outer line. In this manner, a land grid array (LGA) package,including external terminals arranged in two lines like a hound's-toothcheck, is formed. Alternatively, an LGA package, including two lines ofparallelly arranged external terminals, may also be formed.

[0077] In addition, according to the inventive method for manufacturinga resin-molded semiconductor device, land electrodes are arranged in twolines for two different types of leads. Thus, it is also possible toprovide connection portions on the outer side faces of the package. Thatis to say, since the resin-molded semiconductor device can be bondedonto a motherboard on two sides (i.e., bottom and side faces), thedevice can be bonded much more strongly and reliably.

[0078] Embodiment 2

[0079] The leadframe structure of the first embodiment still has someparts to be further modified.

[0080] Hereinafter, modifications applicable to the leadframe of thefirst embodiment will be described with reference to the accompanyingdrawings. FIGS. 14(a) and 14(b) are respectively partial plan view andpartial cross-sectional view illustrating, on a larger scale, part ofthe land lead 4 (i.e., lead on the second line) of the leadframeaccording to the first embodiment. FIGS. 15 and 16 are partialcross-sectional views illustrating how the land lead 4 and lead 5 areaffected by a stress applied by a resin encapsulant being injectedduring a resin molding process. FIG. 17 is a partial cross-sectionalview illustrating what resin-molded semiconductor device will be formedwhen the stress is applied to those leads 4 and 5.

[0081] As shown in FIGS. 14(a) and 14(b), the land lead 4 (i.e., thelead of the second group) has the land portion 8 at its inner end andonly the bottom of the land portion 8 will be the land electrode 16.During a resin molding process, the outer end of the land lead 4 (i.e.,the end located closer to the frame rail) is pressed by a first upperdie 21 against a second lower die 22 via the seal sheet 20 as shown inFIG. 15. However, since the land portion 8 at the inner end of the landlead 4 is relatively distant from the point where the land lead 4 ispressed by the first die 21, the land electrode 16 on the bottom of theland portion 8 cannot strongly adhere to the seal sheet 20. Accordingly,while a resin encapsulant is being injected in the direction indicatedby the arrows in FIG. 15, the injection pressure is likely to lift theland electrode 16 on the bottom of the land portion 8 of the land lead 4from the seal sheet 20. As a result, the land lead 4, which has beenpeeled off the seal sheet 20, will be molded with the resin encapsulantas it is. On the other hand, the inner end of the lead 5 (i.e., lead ofthe first group) is relatively close to a point where the lead 5 ispressed by the first die 21. Thus, when the first die 21 is presseddownward, the bottom of the lead 5 will make tight contact with the sealsheet 20 and is not peeled off the sheet 20.

[0082] If the land lead 4 in such a state is molded with the resinencapsulant, then the resin encapsulant will reach the bottom of theland lead 4 (i.e., the land electrode 16) to leave resin bur 23 on thesurface of the land electrode 16 of the land lead 4 as shown in FIG. 17.As a result, the land electrode 16 could not function as an externalelectrode properly. Thus, to solve a problem like this by getting thebottom of the land lead 4 strongly adhered to the seal sheet 20 andthereby eliminating the resin bur 23 will have a great significance inthe pertinent art.

[0083] Hereinafter, a leadframe designed to solve this problem and amethod for manufacturing a resin-molded semiconductor device using theleadframe will be described with reference to the accompanying drawings.In the following illustrative embodiment, a technique of getting theland electrode 16 of the land lead 4 strongly adhered to the seal sheetwill be exemplified.

[0084] FIGS. 18(a) and 18(b) are respectively plan view andcross-sectional view illustrating a land lead for a leadframe accordingto the second embodiment. The overall structure of the leadframe isbasically the same as that illustrated in FIG. 1. However, the leadframeof the second embodiment is different from the counterpart of the firstembodiment in the shape and function of the land leads 4, i.e., theleads of the second group. As will be described later, according to thisembodiment, at least the land leads 4 are designed to be strongly forcedinto and adhered to the seal sheet. In FIG. 18(b), the dashed lineindicates the lead 5, i.e., the lead of the first group, to show thelevel difference between the lower surface of the land electrode 16 andthat of the lead 5.

[0085] As described above, the leadframe of the second embodiment hasbasically the same structure as that of the first embodiment. Thus, onlythe differences between these two embodiments will be described. As inthe first embodiment, the leadframe of the second embodiment alsoincludes the land leads on the inner line (i.e., the leads of the secondgroup) and the leads on the outer line (i.e., the leads of the firstgroup). However, according to the second embodiment, the land lead 4 hasa different shape as shown in FIGS. 18(a) and 18(b). More specifically,at least the land portion 8 of the land lead 4 is thicker than the otherportion thereof, and the part of the land portion 8, including the landelectrode 16 on the bottom, protrudes downward compared to the lowersurface of the lead 5. That is to say, the land lead 4 has a half-cutportion 24, which is formed by half-cut pressworking, at around the rootof the land portion 8, and the land portion 8 has been pressed down inits entirety. Accordingly, the lowermost edge of the land electrode 16is lower than the bottom of the lead 5 by the space S that is shown inFIG. 18(b) and corresponds to the depth of the half-cut portion 24.

[0086] Furthermore, according to this embodiment, the entire landportion 8 is inclined downward at an angle θ with the principal surfaceof the leadframe. Accordingly, compared to a leadframe structure inwhich the entire land portion 8 is parallel to the principal surface ofthe leadframe, the lower edge of the land portion 8 can be forced intoand adhered to the seal sheet more easily. In this case, the angle θ ofinclination is preferably between 3 and 15 degrees, more preferably 5±1degrees as defined in this embodiment. The level difference of thehalf-cut portion 24, formed by pressworking, is 20 μm. The land lead 4further includes a wide portion 25 connected to the land portion 8. Thewide portion 25 is formed by pressing and extending the land lead 4horizontally.

[0087] In the embodiment illustrated in FIGS. 18(a) and 18(b), thehalf-cut portion 24 is formed at around the root of the land portion 8of the land lead 4, the entire land portion 8 has been pressed down toincline downward at the angle θ and the bottom of the land electrode 16is lower than that of the lead 5. Accordingly, in the resin moldingprocess, the pressure applied by the die strongly forces the bottom ofthe land lead 4, which will be the land electrode 16, into the sealsheet, and the bottom of the land lead 4 can make tight contact with theseal sheet without being lifted from the sheet. As a result, no resinencapsulant reaches, and no resin bur will be left on, the landelectrode 16 of the land lead 4.

[0088] The level difference created by forming the half-cut portion 24can be appropriately defined according to this embodiment depending onthe distance between one end of the land lead 4, connected to the framerail, and the other free end thereof and the pressure applied by thedies. Normally, if the thickness of the land lead 4 is about 200 μm, alevel difference of about 20 μm is preferably formed by half-cutpressworking.

[0089] Next, an exemplary method for manufacturing a resin-moldedsemiconductor device using the leadframe of the second embodiment willbe described.

[0090] In the manufacturing process of the resin-molded semiconductordevice using the leadframe of the second embodiment, almost the sameprocess steps as those of the first embodiment illustrated in FIGS. 8through 13 will be performed. Thus, it will be described just how theland lead 4 changes its position during the resin molding process.

[0091]FIG. 19 is a cross-sectional view how the land electrode 16 of theland lead 4 can make tight contact with the seal sheet 20 during a resinmolding process using the leadframe of the second embodiment.

[0092] As shown in FIG. 19, the land portion 8 of the land lead 4 hasbeen pressed down to be bent downward at the angle θ with the principalsurface of the leadframe and its land electrode 16 has been pressedagainst, and strongly forced into, the seal sheet 20. Thus, the landelectrode 16 can make tight contact with the seal sheet 20.

[0093] In the resin molding process using the seal sheet 20, at leastthe ends of the leads 5 and land leads 4 (i.e., the leads of the firstand second groups) are pressed by the dies to force the land electrodes16 of the leads 5 and land leads 4 into the seal sheet 20. In such astate, the respective members on the upper surface of the leadframe,i.e., the upper part of the die pad, the semiconductor chip and themetal fine wires, are molded together with the resin encapsulant. Whenthis pressure is applied, the land electrodes 16 of the leads 5 arepressed against the seal sheet 20. Thus, the land electrodes 16 of theland leads 4, which have been pressed down to incline downward at theangle θ with the principal surface of the leadframe, are also pressedagainst and strongly forced into the seal sheet 20. As a result, theresin molding process can be performed with no resin encapsulant allowedto reach the land electrodes 16.

[0094] Thus, it is possible to prevent the land leads 4 from beinglifted from the seal sheet 20. Since no gap is formed between the sealsheet 20 and the land electrodes 16 of the land leads 4, no resinencapsulant will reach, and no resin bur will be left on, the landelectrodes 16. In FIG. 19, the arrow indicates that the pressure,applied by the resin encapsulant being injected, forces the landelectrode 16 of the land lead 4 into the seal sheet 20.

[0095] Next, it will be described with reference to FIGS. 20 and 21 howto shape the land lead of the leadframe according to the secondembodiment. FIGS. 20 and 21 are cross-sectional views illustrating theland lead along with upper and lower dies.

[0096] First, as shown in FIG. 20, a relatively thick lead member 26, ofwhich a land lead will be made, is sandwiched between upper and lowerdies 29 and 32 and then shaped by pressworking. The upper die 29includes a half-cut pressworking portion 27, inclined at the desiredangle, and a pressing portion 28 for pressing and extending the leadmember 26. On the other hand, the lower die 32 includes a concaveportion 30 and a pressing portion 31, which correspond to the half-cutpressworking portion 27 and pressing portion 28 of the upper die 29,respectively.

[0097] In this case, the shapes of the half-cut pressworking portion 27and concave portion 30 of the upper and lower dies 29 and 32 are definedsuch that the land portion and half-cut portion will be formed at theend of the lead member 26 and at the root of the land portion,respectively, and that the entire land portion will be pressed down andinclined downward at the angle θ with the principal surface of theleadframe. Also, except for parts of the lead member 26 connected to theland portion and the frame rail of the leadframe, respectively, the leadmember 26 is pressed and extended horizontally (i.e., compressedvertically) by the pressing portions 28 and 31 of the upper and lowerdies 29 and 32. As a result, that pressed part of the lead member 26 hasits thickness reduced and extended horizontally to form the wideportion.

[0098] As shown in FIG. 21, except for at least the land portion 8 andthe inner end 33, the land lead 4 is relatively thin, and the landportion 8 including the land electrode 16 protrudes and inclinesdownward at the angle θ. In this land lead 4, the half-cut portion 24 isformed by half-cut pressworking at around the root of the land portion8, the land portion 8 itself has been pressed down and the landelectrode 16 thereof is lower than that of the lead 5. In theillustrated embodiment, the thinned portion of the land lead 4 has athickness of 130 μm when the lead member 26 has a thickness of 200 μm.That is to say, a level difference of 70 μm has been formed. On theother hand, the land portion 8 has a level difference of 20 μm, whichhas been created by the half-cut portion 24, and has been pressed down.The angle θ of inclination may be 5±1 degrees as described above.

[0099] By manufacturing a resin-molded semiconductor device using theleadframe of this embodiment, almost no resin bur will be left on theland electrodes 16 of the land leads 4 during the resin molding process.As a result, the land electrodes will stick out of the resin encapsulantto reach a sufficient standoff height in the resin-molded semiconductordevice.

[0100] In the foregoing embodiments, the leadframe is supposed to havethe leads arranged in two lines, i.e., the leads of the first and secondgroups. However, according to the present invention, those leads do nothave to be arranged in two lines but in any other number of lines. Thus,the present invention is effectively applicable to a leadframe withleads arranged in three, four or more lines.

[0101] By forming a resin-molded semiconductor device using theinventive leadframe, a land grid array (LGA) package, having externalterminals arranged in two lines on its bottom, can be obtained withalmost no resin bur left on the bottom. Also, according to the presentinvention, the land electrodes can be formed out of the leadframe on thebottom of the resin-molded semiconductor device without using anyadditional circuit board for the electrodes. As a result, themanufacturing costs can be cut down, and yet the device can be bondedonto a motherboard more reliably compared to the known bonding techniqueusing leads.

[0102] In accordance with the inventive method for manufacturing aresin-molded semiconductor device, the resin molding process isperformed using the leadframe and with the seal sheet adhered to thebottom of the leadframe. That is to say, there is no need to form anyprotruding leads unlike the known process. Thus, the lead bendingprocess can be omitted. In addition, after the resin molding process isfinished, the land leads will have their land electrodes exposed alongthe inner line on the bottom of the package and the leads will also havetheir land electrodes exposed along the outer line on the bottom. Inthis manner, two lines of external terminals can be arranged parallellyor like a hound's-tooth check, thus providing an LGA package.Furthermore, the land electrodes, arranged along the outer line on thebottom of the resin-molded semiconductor device, are parts of the leadsand the outer side faces of those leads are exposed out of the package.Thus, by applying an adhesive such as solder to these side faces, filletportions will be formed and the package can be bonded onto a motherboardon two sides, i.e., on the bottom and side faces. As a result, thepackage can be bonded more strongly and connected more reliably onto themotherboard.

What is claimed is:
 1. A method for manufacturing a resin-moldedsemiconductor device, comprising the steps of: a) preparing a leadframe,the leadframe including: a frame rail made of a metal plate; a die padfor mounting a semiconductor chip thereon, the die pad being disposedapproximately in a. center region of an opening of the frame rail;support leads, one end of each said support lead supporting the die pad,the other end of the support lead being connected to the frame rail; afirst group of leads, one end of each said lead of the first groupextending toward the die pad at least partially, the other end of thelead of the first group being connected to the frame rail, the bottom ofthe lead of the first group being used as a land electrode of a firstgroup; and a second group of leads, one end of each said lead of thesecond group extending toward the die pad and being closer to the diepad than the end of each said lead of the first group is, the other endof the lead of the second group being connected to the frame rail, partof the bottom of the lead of the second group being used as a landelectrode of a second group, wherein the first and second groups of landelectrodes are arranged in two lines, and wherein part of each said leadof the second group has been pressed down by half-cut pressworking suchthat the bottom of each said land electrode of the second group is lowerthan the bottom of each said land electrode of the first group, andwherein said part of the lead of the second group is inclined downward;b) bonding a semiconductor chip onto the die pad of the leadframeprepared; c) connecting electrode pads, which are formed on theprincipal surface of the semiconductor chip bonded to the die pad, torespective upper surfaces of the first and second groups of leads of theleadframe with metal fine wires; d) adhering a seal sheet to at leastthe bottoms of the die pad and the first and second groups of leads onthe back-side of the leadframe; e) molding an upper part of theleadframe, the semiconductor chip, the die pad and the metal fine wirestogether with a resin encapsulant, while applying a pressure to at leastthe ends of the first and second groups of leads to press the first andsecond groups of land electrodes against the seal sheet; and f)stripping the seal sheet from the leadframe after the step e) has beenperformed.
 2. The method of claim 1, wherein in the step e), when thefirst group of land electrodes are pressed against the seal sheet withthe pressure applied, the second group of land electrodes are pressedagainst, and forced into, the seal sheet.